PhD researcher provides ways to determine methane emissions on land

Nadine Smit, researcher at the Royal NIOZ Netherlands Institute for Sea Research, has discovered new chemical tracers to investigate the presence of terrestrial bacteria that consume the powerful greenhouse gas methane. The knowledge about methane emissions and its consequences in the deep geological past can help predict possible consequences of higher future concentrations of greenhouse gas for life on Earth. Smit will defend her PhD dissertation at Utrecht University on Friday 27 August.

At Royal NIOZ, much research is done on so-called marine lipid biomarkers, tracers that are left behind by micro-organisms like marine bacteria and archaea, and are important indicators for climate research: they tell the scientists for example how much greenhouse gases like CO2 or methane are stored in ocean sediments or how much is released by hydrocarbon seepage into the water column and subsequently, into the atmosphere.

Terrestrial gas seeps on Sicily

To mitigate global warming, it is crucial to better understand both the sources and sinks of greenhouse gases in the oceans and on land. Rising methane concentrations come from natural sources like gas seeps, however, much larger amounts are emitted by industry and escape from methane stores in melting permafrost. During her PhD research at NIOZ and Utrecht University, organic geochemist Nadine Smit focused on the part of the carbon cycle that is situated on land.

“On land”, Smit says, “soils are one of the biggest microbial sinks for atmospheric methane, but only a few unambiguous biomarkers are known that can help us trace methane-consuming bacteria in terrestrial environments with a lot of oxygen.”

Macculabe moddervulkaan op Sicilië
In gas seeps on Sicily, Nadine Smit found new bacteria that live on the greenhouse gases methane and ethane.

Smit collected soil samples of the different terrestrial gas seeps like an Everlasting Fire on the Mediterranean island Sicily. “At these sites, much greenhouse gas is emitted, increasing the activity of bacteria that feed on the strong greenhouse gases methane and ethane. My samples provide insight into the gradient of microbes away from the methane source.”

Several new biomarkers

Smit found new biomarkers for several different types of methane- consuming and, surprisingly also ethane-consuming, bacteria. “In the Everlasting Fire, we found so-called mycobacteria, which are related to tuberculosis bacteria, and which have never before been related to these kinds of gas seeps. According to my analyses, they are most probably living on ethane that is emitted from the natural gas seep.”

During the coming years, the stability of the new biomarkers has to be determined. Smit: “If they indeed turn out to be stable, they will offer a new method to analyze the land-dwelling micro-organisms that consumed methane and ethane now and in the geological past.” This would enable researchers to predict the possible consequences of higher future concentrations of greenhouse gas for life on Earth.

Nadine Smit will defend her dissertation during a hybrid meeting at Utrecht University on Friday 27 August at 10.15 am. You are welcome to join via a livestream.